It is often advantageous to prepare a halogenated ester by addition of a halogenated nucleophile to an alcohol-derived diester. If only one of the oxyanionic alcohol residues is displaced from the carbonyl carbon of the diester by the halogenated nucleophile, the desired ester results. If, however, both oxyanionic residues are displaced, a ketone byproduct results instead. A mixture of the desired ester and the ketone byproduct is usually obtained from this type of addition reaction.
In Wiley, U.S. Pat. No. 2,988,537, a method is described in which, in the presence of an alkoxide ion, a halogenated, ethylenically unsaturated olefin can be added to either a mono- or diester or a carboxamide. The results of the experimental work disclosed in Wiley recognize that when such addition is made to a carbonate ester, a mixture is obtained of an ester to which one equivalent of halogenated olefin has been added, and a ketone to which two equivalents of the olefin have been added. However, there is no indication in Wiley that one of those products is sought in preference to the other. The method of Wiley consequently does not offer any guidance as to how ester synthesis by halogenated olefin addition can be operated to obtain a desirably high, and preferably maximum, yield of the ester while holding the quantity of the ketone to as low a level as possible.
It would consequently be desirable to have a process which would allow nucleophilic addition of a halogenated olefin to a diester with a resulting preferential yield of a high ratio of ester product to ketone byproduct.